Method of producing aromatic carboxylic acids from alkylbenzenes

ABSTRACT

A process for the preparation of aromatic carboxylic acids by the oxidation of alkyl benzenes with oxygen or gases containing molecular oxygen in an aliphatic carboxylic acid environment and in the presence of catalysts consisting of the salts of heavy metals in which the oxidation is carried out in the presence as an activator of an organic compound in which the molecule contains both keto and hydroxy groups.

United States Patent Reni et a1.

[ June 27, 1972 METHOD OF PRODUCING AROMATIC CARBOXYLIC ACIDS FROMALKYLBENZENES,

Cesare Reni, Busto Arsizio; Luigi Lugo, Milan; Giorgio Gualdi, Verona,all of Italy Assignee: Socleta ltaliana Resine S.p.A., Milan, ItalyFiled: June 30, 1970 Appl. No.: 51,364

Inventors:

Foreign Apflication Priority Data July 7, 1969 Italy ..19283 A/69 U.S.Cl. ..260/524 R, 252/428, 252/429 R ..C07c 63/02 Field of Search ..260/524 R References Cited UNITED STATES PATENTS 6/1968 Alagy ..260/5242,245,528 6/1941 Loder ..260/524 2,883,421 4/1959 Speer ..260/524 OTHERPUBLICATIONS Fieser et al., Organic Chemistry, 3rd Edition, 1956, pages207- 9.

Florin et al., J. Research of National Bur. Stds. 72A( 1 February, 1968,pages 49, 72 and 73.

Primary Examiner-Lorraine A. Weinberger Assistant Examiner-R. S.Weissberg Attorney-Sughrue, Rothwell, Mion, Zinn & Macpeak [57] ABSTRACT12 Claims, No Drawings METHOD OF PRODUCING AROMATIC CARBOXYLIC ACIDSFROM ALKYLBENZENES This invention relates to an improved process for theproduction of aromatic carboxylic acids by the oxidation of alkylbenzenes in liquid phase in the presence of catalysts.

There are various known methods of catalytic oxidation of alkyl benzenesin an inert liquid environment, in which, for example, xylenes areconverted into the corresponding phthalic acids, toluene into benzoicacid and p-diisopropyl benzene into terephthalic acid.

The products thus obtained are extremely useful to industry.

Terephthalic acid, for example, normally in diester form, is converted,in conjunction with glycols, into polymers that can be used in theproduction of yarns.

Thus, in one well-known process, p-xylene is oxidized to form p-toluicacid, which is subjected to further oxidation after esterification ofthe carboxyl group, normally with methanol.

In other familiar processes, alkyl benzenes are oxidized to form thecorresponding carboxylic acids, inert solvents being used, in thepresence of catalysts consisting of the salts of heavy metals.

With such processes, however, in which use is also made of reactionactivators normally consisting of bromine and derivatives thereof, theconversion rates and oxidation selectivity are relatively poor; nor arebetter results obtained when different activators are employed, such as,for instance, organic compounds in which the molecule contains aldehydeor ketone carbonyl groups.

In some cases, therefore, the unconverted compounds are partiallyrecovered and subjected to further oxidation by, for example, treatmentwith nitric acid.

The oxidation process thus becomes burdensome, with obvious economicdisadvantages.

One object of the present invention is therefore the provision of aprocess for the catalytic oxidation of alkyl benzenes in liquid phase,in which high speeds of reaction are possible, as well as high rates ofconversion to aromatic carboxylic acids.

The scope of the invention also includes a process for the catalyticoxidation of alkyl benzenes in liquid phase to form aromatic carboxylicacids such as require only simple purification treatment to yieldproducts that can be used for the purposes for which they are normallyintended.

Further objects of the invention will become apparent from thedescription which follows.

The process here proposed consists essentially in oxidizing by means ofoxygen or gases containing molecular oxygen, alkyl benzenes in analiphatic carboxylic acid environment, in the presence of heavy metalsalts, the activators employed being organic compounds in which themolecule contains keto and hydroxyl groups.

According to the proposed process, to be more precise, an alkyl benzeneor a group of alkyl benzenes is subjected to oxidation in the presenceof an aliphatic carboxylic acid that is liquid in the conditions ofreaction.

The carboxylic acids preferred are acetic and propionic acids, used inthe proportion of one to parts by weight to each part by weight of alkylbenzene.

The catalysts for the oxidizing reaction consist of heavy metal salts,among which preference should be given to the salts of cobalt andmanganese, normally to be used in acetate or halide form.

The catalytic salts are added to the reaction environment in theproportion of 0.1 to 5.0 parts by weight to every 100 parts by weight ofthe alkyl aromatic hydrocarbon that is to be oxidized.

As already stated, the purposes of the invention are achieved byemploying as activators organic compounds in which the molecule containsalcohol groups and ketone groups, preferably diacetone alcohol, whichhas shown itself to be the most active and selective in the oxidation ofalkyl benzenes.

It has been found that the best results are obtained when theconcentration of the activator is maintained at a level of between 0.5and 5.0 by weight in the reaction mixture.

By the use of such activators, the xylenes are oxidized to form thecorresponding phthalic acids, the conversion rate equalling or exceeding93 percent in mols, when the reaction takes place at temperatures of C.to 160 C. and pressures of 5 to 30 atmospheres, the oxidizing gas beingoxygen or gases containing molecular oxygen.

By the method here proposed, it is also possible for toluene to beoxidized to benzoic acid and p-diisopropyl benzene to terephthalic acid.

The oxidizing reaction may be carried out either discontinuously or(preferably) continuously.

Where the process is continuous, elongated reaction vessels equippedwith agitators may be used.

The alkyl benzene or mixture of alkyl benzenes, the carboxylic acid andthe catalyst consisting of salts of one or more heavy metals areadmitted to the top of the reaction vessel, while the oxidizing gas,preferably air, is fed to the base at a rate such that the gases at thetop of the vessel contain between 1 percent and 5 percent of oxygen.

The whole or only part of the activator may be added at the top of thevessel; in the latter case, several points of admission may be usedalong the body of the vessel.

The following examples of experiments will serve as a betterillustration of the process, but they should not be held to imply anylimitation on the scope of the invention.

EXAMPLE 1 An elongated tubular reaction vessel of about 10 literscapacity was used, this being equipped with effective agitation, aheat-exchange jacket and arrangements for introducing the reagents andremoving the reaction products.

The top of the vessel was also fitted with facilities for condensing andre-cycling condensable products.

The following were fed continuously to the top of the reaction vessel:0.8 liters/hour of p-xylene, 4 liters/hour of acetic acid (97 percentcone.) and 100 mL/hour of an aqueous solution containing g./liter ofcobalt bromide and 150 g./liter of manganese bromide. Diacetone alcoholwas also fed to the top of the vessel at the rate of 90 ml./hour, asecond similar feed being provided approximately half-way up the vessel.

Air was fed to the base of the reaction vessel at the rate of about2,300 N. liters an hour.

The working temperature and pressure were 130 C. and 9 atmospheres.

The reaction products were removed continuously from the base of thevessel, terephthalic acid being recovered from these and washed withwater and acetic acid.

By this means, an average of about 1 kg./hour of pure terephthalic acidwas obtained.

EXAMPLE 2 (comparative).

The same procedure was followed as in Example 1, except that thediacetone alcohol was omitted.

By this means, the rate of conversion of the p-xylene to terephthalicacid was less than 80 percent in mols.

What we claim is:

1. In a process for the production of aromatic carboxylic acidsconsisting essentially of oxidizing, in a reaction zone, alkyl benzenesand mixtures thereof employing an oxidizing gas comprising oxygen or agas containing molecular oxygen in the presence of an aliphaticcarboxylic acid reaction solvent, said aliphatic carboxylic acid beingliquid under the reaction conditions existing in the reaction zone,employing a catalytic amount of a heavy metal salt catalyst and anactivator therefor, collecting the reaction products from the reactionzone and separating therefrom the product aromatic carboxylic acidcorresponding to the alkyl benzene feed, the improvement consistingessentially of conducting the oxidation reaction at a temperature offrom 100 to C and at a pressure of from 5 to 30 atmospheres employing anactivator consisting essentially of diacetone alcohol.

2. The process of claim 1 wherein said aliphatic carboxylic acid isacetic or propionic acid.

3. The process of claim 2 wherein said aliphatic carboxylic acid isemployed in a proportion of from one to parts by weight to each part byweight of said alkyl benzenes.

4. The process of claim 1 wherein said catalyst is a salt of cobalt ormanganese and is employed in a proportion of from 0.1 to 5.0 parts byweight to every 100 parts by weight of said alkyl benzenes.

5. The process of claim 4 wherein said catalyst is a halide or acetatesalt of cobalt or manganese.

6. The process of claim 1 wherein said alkyl benzene comprisespara-xylene and wherein the corresponding aromatic carboxylic acid isterephthalic acid.

7. The process of claim 1 wherein said alkyl benzene comprises tolueneand wherein the corresponding aromatic carboxylic acid comprises benzoicacid.

8. The process of claim 11 wherein said alkyl benzene comprisespara-diisopropyl benzene and wherein the correspond ing aromaticcarboxylic acid comprises terephthalic acid.

9. The process of claim 1 wherein said oxidizing gas is air and whereinthe air is fed tothe reaction zone in an amount such that the gasexiting from the top of the reaction zone comprises between 1 and 5weight percent oxygen.

10. The process of claim 1 wherein the reaction is conducted in anelongated reaction vessel, wherein the alkyl benzenes, catalysts, andaliphatic carboxylic acid are fed to the top thereof, and wherein only aportion of said activator is fed to the top of said reaction vessel, theremaining portion of the activator being fed to the reaction vessel at apoint along the body thereof.

1 1. The process of claim 1 wherein said diacetone alcohol is fed to thereaction zone in an amount sufficient to maintain a concentration ofsaid diacetone alcohol in said reaction zone of from 0.5 to 5.0 parts byweight per parts of said alkyl benzenes.

12. In a process for the production of terephthalic acid consistingessentially of oxidizing, in a reaction zone, para-xylene with air inthe presence of from one to 10 parts by weight to every part by weightof said para-xylene of an aliphatic carboxylic acid reaction solventcomprising acetic or propionic acid, employing from 0.1 to 5 parts byweight to every 100 parts by weight of said para-xylene of a catalystcomprising a halide or acetate salt of cobalt or manganese and anactivator therefor, collecting the reaction product from the reactionzone and separating therefrom the product terephthalic acid, theimprovement consisting essentially of conducting the oxidation reactionat a temperature of from 100 to C and at a pressure of from 5 to 30atmospheres employing from 0.5 to 5 parts by weight per 100 parts byweight of said paraxylene of an activator consisting essentially ofdiacetone alcohol.

2. The process of claim 1 wherein said aliphatic carboxylic acid isacetic or propionic acid.
 3. The process of claim 2 wherein saidaliphatic carboxylic acid is employed in a proportion of from one to 10parts by weight to each part by weight of said alkyl benzenes.
 4. Theprocess of claim 1 wherein said catalyst is a salt of cobalt ormanganese and is employed in a proportion of from 0.1 to 5.0 parts byweight to every 100 parts by weight of said alkyl benzenes.
 5. Theprocess of claim 4 wherein said catalyst is a halide or acetate salt ofcobalt or manganese.
 6. The process of claim 1 wherein said alkylbenzene comprises para-xylene and wherein the corresponding aromaticcarboxylic acid is terephthalic acid.
 7. The process of claim 1 whereinsaid alkyl benzene comprises toluene and wherein the correspondingaromatic carboxylic acid comprises benzoic acid.
 8. The process of claim1 wherein said alkyl benzene comprises para-diisopropyl benzene andwherein the corresponding aromatic carboxylic acid comprisesterephthalic acid.
 9. The process of claim 1 wherein said oxidizing gasis air and wherein the air is fed to the reaction zone in an amount suchthat the gas exiting from the top of the reaction zone comprises between1 and 5 weight percent oxygen.
 10. The process of claim 1 wherein thereaction is conducted in an elongated reaction vessel, wherein the alkylbenzenes, catalysts, and aliphatic carboxylic acid are fed to the topthereof, and wherein only a portion of said activator is fed to the topof said reaction vessel, the remaining portion of the activator beingfed to the reaction vessel at a point along the body thereof.
 11. Theprocess of claim 1 wherein said diacetone alcohol is fed to the reactionzone in an amount sufficient to maintain a concentration of saiddiacetone alcohol in said reaction zone of from 0.5 to 5.0 parts byweight per 100 parts of said alkyl benzenes.
 12. In a process for theproduction of terephthalic acid consisting essentially of oxidizing, ina reaction zone, para-xylene with air in the presence of from one to 10parts by weight to every part by weight of said para-xylene of analiphatic carboxylic acid reaction solvent comprising acetic orpropionic acid, employing from 0.1 to 5 parts by weight to every 100parts by weight of said para-xylene of a catalyst comprising a halide oracetate salt of cobalt or manganese and an activator therefor,collecting the reaction product from the reaction zone and separatingtherefrom the product terephthalic acid, the improvement consistingessentially of conducting the oxidation reaction at a temperature offrom 100* to 160* C and at a pressure of from 5 to 30 atmospheresemploying from 0.5 to 5 parts by weight per 100 parts by weight of saidpara-xylene of an activator consisting essentially of diacetone alcohol.